Process for the production of an aqueous monoester peroxycarboxylic acid solution, the solution obtainable by this process, and its use as disinfectant

ABSTRACT

Process for the production of an aqueous monoester peroxycarboxylic acid solution by reaction of a peroxygen compound with at least one dicarboxylic acid and with at least one alcohol optionally in the presence of an acid catalyst. Aqueous monoester peroxycarboxylic acid solution obtainable by this process. Use of the aqueous monoester peroxycarboxylic acid solution as disinfectant.

The present invention is related to a process for the production of anaqueous monoester peroxycarboxylic acid solution. It also concerns theaqueous monoester peroxycarboxylic acid solution obtainable by thisprocess and its use in disinfectant compositions.

Compositions containing monoester percarboxylic acids and theirpreparation by reaction between a monoester of an aliphatic dicarboxylicacid and hydrogen peroxide have been described in the internationalpatent application WO 95/34537 to SOLVAY INTEROX LIMITED. Suchcompositions were shown to have no discernible odour and to be effectiveas microbicide. Although the compositions exhibited a level of availableoxygen stability that would enable them to remain effective duringseveral months storage, there is a continuing need to find new solutionsof monoester percarboxylic acids.

It is an object of the invention to provide a new or alternative processfor the production of monoester peroxycarboxylic acid solutions as wellas to provide new monoester peroxycarboxylic acid solutions.

Consequently, the present invention concerns a process for theproduction of an aqueous monoester peroxycarboxylic acid solution byreaction of a peroxygen compound with at least one polycarboxylic acidand with at least one alcohol optionally in the presence of an acidcatalyst. Preferably, the polycarboxylic acid is a dicarboxylic acid.While focused on this preferred embodiment, the present invention ishowever not limited thereto.

One of the essential characteristics of the process of the inventionresides in the nature of the starting materials especially thedicarboxylic acid and the alcohol which render the process particularlyperforming. Indeed, by using these starting materials new solutions canbe produced. It will be recognised that a complex mixture will beobtained using the process according to the invention containing thedesired monoester peroxycarboxylic acid (called ester peracidhereafter), water, and may also contain residual amounts of non consumeddicarboxylic acid (called diacid hereafter), peroxygen compound, alcoholand optional acid catalyst, and in situ generated corresponding diester,monoester carboxylic acid, monocarboxylic peroxycarboxylic acid anddiperoxycarboxylic acid. The advantage of the process of the inventionresides in the possibility to control the relative amounts of thedesired ester peracid to all the other products generated in situ.Indeed, by varying the amount of alcohol in the reaction mixture, moreor less of the ester peracid will be produced relative to the amount ofother products. So, a large variety of solutions can be obtained using asingle process.

Another advantage resulting from the nature of the stating materialsresides in the duration of the process. Indeed, the diacids used asstarting material in the present invention have generally a highersolubility in the reaction mixture than have monoesters of dicarboxylicacids which are used in the known process described in the internationalpatent application WO 95/34537. The higher solubility results in fasterdissolution rates and thus shorter production times.

Yet another advantage of the process of the invention resides in theavailability of the stating materials. Indeed, diacids and alcohols aremore readily available than monoesters of a dicarboxylic acid.

Yet another advantage of the process of the present invention resides inthe large choice of the organic radical of the ester group. Indeed, inthe known process of the international patent application WO 95134537the choice of the organic radical of the ester group is determined bythe choice of the monoester of a dicarboxylic acid used as startingmaterial whereas in the present invention the organic radical of theester group originates from the alcohol It is clear that in the processof the invention alcohols can be used which are not available asmonoesters.

The diacid used in the process of the invention can be chosen from anycompound containing at least two carboxylic acid groups and which iscapable of being transformed in an ester peracid in the process of theinvention. The diacid can contain up to 20 carbon atoms, preferably upto 10 carbon atoms. The principal chain of the diacid which issubstituted by the two carboxylic groups can be linear, branched, cyclicor aromatic, optionally unsaturated and or containing a heteroatom.Oxalic acid is convenient. Diacids with a linear principal chaingenerally corresponding to the formula COOH—R—COOH in which R is analkylene group containing up to 6 carbon atoms can also be used.Suitable examples are adipic acid, glutaric acid and succinic acid.Examples of diacids with a branched principal chain are methyl succinicand ethyl malonic acids. Other examples are maleic, fumaric and maleicacids. The preferred diacids are adipic, glutaric and succinic acids. Amixture of two or more different diacids can be used in the process ofthe invention.

The diacid is generally used in an amount of at least 0,05% wt of thereaction mixture, preferably at least 5% wt The amount of diacid used isusually at most 65% wt in particular at most 25% wt. Quantities from0,05 to 65% wt of diacid are convenient.

The peroxygen compound used in the process according to the inventioncan be chosen from hydrogen peroxide or any other peroxygen compoundcapable of releasing hydrogen peroxide in the reaction mixture of theprocess of the present invention. The expression “reaction mixture ofthe process of the invention” means a mixture containing water, thediacid, the alcohol, the peroxygen compound, optionally the acidcatalyst, the ester peracid, the corresponding diester, monoestercarboxylic acid, monocarboxylic peroxycarboxylic acid anddiperoxycarboxylic acid. In particular, the peroxygen compound can bechosen from hydrogen peroxide, inorganic peracids, organic peracids andpersalts. An example of inorganic peracid is Caro's acid. Organic acidscontaining up to 10 carbon atoms are convenient. An example of such anorganic peracid is peracetic acid. Examples of persalts are sodiumpercarbonate and sodium perborate mono- or tetrahydrate. Hydrogenperoxide is preferred.

The peroxygen compound is generally used in an amount of at least 0,01%wt of the reaction mixture, in particular at least 5% wt. The amount ofperoxygen compound used is usually at most 30% wt of the reactionmixture, preferably at most 25% wt. Quantities of peroxygen compoundfrom 0,05 to 30% wt are convenient. When hydrogen peroxide is used, itcan be added to the reaction mixture in the form of an aqueous solutioncontaining from 1 to 85% wt of hydrogen peroxide. The molar ratio of theperoxygen compound to the diacid can be varied in a wide range.Generally this molar ratio is at least 0,1:1, preferably at least 1:1.The molar ratio is usually at most 35:1, in particular at most 7:1.

The alcohol used in the process of the invention can be chosen from anycompound containing at least one hydroxyl group. Monoalcohols containingup to 20 carbon atoms are suitable, those containing up to 10 carbonatoms are preferred. Examples of suitable monoalcohols are methanol andethanol. Diols containing up to 20 carbon atoms, preferably up to 10carbon atoms can also be used. Examples of suitable diols are ethyleneglycol and propylene glycoL. Polyols containing up to 20 carbon atomscan also be used. Examples of suitable polyols include sorbitol andmannitol. Alcohol ethoxylates could also be used. A mixture of two ormore different alcohols can be used in the process of the invention.

The alcohol is generally used in an amount of at least 0,01% wt of thereaction mixture, in particular of at least 2% wt. The amount of alcoholused is usually at most 45% wt. more particularly at most 25% wtQuantities of alcohol from 0,05 to 45% wt are convenient. The molarratio of the alcohol to the diacid can be varied within a wide range.Generally the ratio is at least 0,1:1, preferably at least 0,5:1. Themolar ratio is usually at most 10:1, in particular at most 1:1.

The acid catalyst optionally used in the process of the invention can bean inorganic or organic acid having a pKa of about 3 or lower, andpreferably having a pKa of below 1. It is particularly desirable toemploy a non-halide mineral acid such as sulphuric or phosphoric orsulphamic acid or an organic sulphonic acid such as methyl or toluenesulphonic acid or a cation exchange resin doped with acid. Organic acidscan also be used. Those containing up to 10 carbon atoms are convenientAn example of organic acid is citric acid.

The catalyst is desirably used in a concentration of at least 0,05% wtin the reaction mixture, in particular at least 0,1% wt. The acidcatalyst concentration is in many instances at most 10% wt especially atmost 2,5% wt. Quantities of acid catalyst from 0,05 to 10% wt areconvenient.

The invention process can be carried out at ambient temperature or at anelevated temperature. In practice the temperature can be at least 10°C., in particular at least 15° C. When it is desirable to achieveequilibration rapidly temperatures of at least 30° C. can be used. Thetemperature is commonly at most 60° C., especially at most 30° C.

The duration of the invention process can vary within a very wide rangeand depends on whether it is desired to obtain an equilibrium solutionor a nonequilibrium solution. Equilibration can already be reached aftera duration of at least 5 min. The duration is commonly at most 24 h.

The invention process can be carried out in any apparatus adequate formixing the staring materials (diacid, peroxygen compound, alcohol, waterand acid catalyst).

According to the process of the invention the starting materials(diacid, peroxygen compound, alcohol, water and acid catalyst) can beadded in any order.

The reaction mixture can be stirred during the process of the invention.

The process of the invention is very useful for producing aqueousmonoester peroxycarboxylic acid solutions containing the monoesterperoxycarboxylic acid, water, residual amounts of non consumed peroxygencompound, dicarboxylic acid, alcohol and optional acid catalyst, and insitu generated corresponding diester, monoester carboxylic acid,monocarboxylic peroxycarboxylic acid and diperoxycarboxylic acid.

Consequently, the present invention also concerns aqueous monoesterperoxycarboxylic acid solutions obtainable by the process describedabove containing the ester peracid, water, residual amounts of nonconsumed peroxygen compound, one or more diacids, one or more alcoholsand optional acid catalyst, and in situ generated corresponding diester,monoester carboxylic acid, monocarboxylic peroxycarboxylic acid anddiperoxycarboxylic acid. Particularly beneficial solutions are thoseobtainable by the process wherein the amounts of alcohol and diacid usedare such that the molar ratio of hydroxy groups present in the alcoholto the carboxylic acid groups present in the diacid is different from 1.

The pH of the invention solutions can vary in a wide range. The pH isgenerally at least −2, most often at least 1. pH values of at most 8 arepossible, values of at most 5 are preferred.

The concentration of ester peracid in the solution of the invention isgenerally at least 0,001% wt in particular at least 0,005% wt. The esterperacid concentration is usually at most 35% wt, especially at most 5%wt.

The amount of water present in the solution of the invention can varywithin a very wide range since the solutions can be very dilute or veryconcentrated. The water content is commonly at least 10% wt. The amountof water is often at most 90% wt.

The solution of the invention contains in many cases residual amounts ofnon consumed peroxygen compound from 0,1 to 30% wt.

The diacid is usually present in the solution of the invention in aresidual amount of at least 0,05% wt. The amount of diacid is commonlyat most 10% wt The solution of the invention can contain a mixture oftwo or more different diacids.

If residual amounts of alcohol are found in the solution of theinvention, these amounts are commonly at least 0,1% wt The amount ofalcohol is often at most 10% wt. The solution of the invention cancontain a mixture of two or more different alcohols.

The residual amount of optional acid catalyst that can be present in thesolution of the invention is usually from 0 to 5% wt.

The solution of the invention can contain an amount of in situ generateddiester from 0 to 5% wt.

The in situ generated monoester carboxylic acid can be present in thesolution of the invention in an amount from 0 to 10% wt.

The concentration of in situ generated monocarboxylic peroxycarboxylicacid that can be found in the solution of the invention is often from 0to 30% wt.

The amount of in situ generated diperoxycarboxylic acid that can bepresent in the solution of the invention is commonly from 0 to 10% wt.

Particularly beneficial solutions are those containing at least 0,01% wtof monoester peroxycarboxylic acid, at least 0,1% wt of peroxygencompound, at least 0,05% wt of dicarboxylic acid and at least 0,1% wt ofalcohol

The solution of the invention can contain other additives. Theseadditives can be chosen from stabilisers, surfactants and thickeners.Such additives are often incorporated in an amount from 0,02 to 20%, andin many instances from 0,1 to 10% wt of the solution.

Suitable stabilisers include hydroxy substituted aromatic carboxylicacids and ester derivatives thereof particularly phenol carboxylic acidssuch as p-hydroxybenzoic acid and ester derivatives such as methyl orethyl esters. They also include organic polyphosphonic acid sequestrantssuch as ethylidene diphosphonic acid, and aminopolymethylenephosphonicacids, pyridine carboxylic acids especially dipicolinic acid andmixtures thereof. In addition inorganic stabilisers may be used. Anexample of inorganic stabiliser is colloidal tin.

The surfactants can be nonionic, anionic or amphoteric. Surfctants canbe soap or synthetic. Typical examples are described in chapter 2 ofSynthetic Detergents by A. Davidson and B/M. Milwidsky, 6^(th) Editionpublished in 1978 by George Godwin Limited. Cationic surfactants includequaternary ammonium salts, non-halide examples include sulphates,metosulphates, ethosulphates, hydroxides, acetates, saccharinates,phosphates and propionates.

Typical examples of suitable non-surfactant thickeners are cross linkedpolyacrylates, natural gums such as xanthan or rhamsan gum, cellulosederivatives such as carboxymethyl cellulose and silicates.

The solutions of the invention can also contain additional non-halidemineral acids. These acids can be selected from sulphuric, phosphoric orsulphamic acid or an organic sulphonic acid. The acid can be present ata concentration from 0,05 to 10% wt in the solution.

Particularly desirable solutions are those containing up to 20% wt ofsurfactant, from 0,025 to 5% wt of stabiliser and from 0,05 to 10% wt ofa non-halide mineral acid.

The solution of the invention can be advantageously used asdisinfectant. The present invention concerns therefore also the use ofthe above described solutions as disinfectants. The method fordisinfection according to the present invention comprises contacting thesubstrate to be disinfected with the solution as a storage stableaqueous acidic solution of an ester peracid or prepared from one. Thesolution may be employed with or without dilution. When compositions arediluted, dilution is usually chosen to give an ester peracidconcentration in solution of between about 1 part per million and 10000parts per million, depending on the substrate. The disinfecting methodcan use a wide range of temperatures, typically from about 4° C. to theboiling point of the disinfectant. The solution of the invention can beused in a range of disinfection applications: e.g. disinfection ofmicro-organism contaminated aqueous media e.g. process waters containingbacteria, algae, yeasts and viruses from industries such as paper andpulp, food processing e.g. sugar refining, brewing, wine making,discharges from sewage treatment works, meat processing factories,carcase rendering and livestock rearing. Other substrates includeirrigation water in the horticultural industry, contaminated coolingwaters, and contaminated surfaces in e.g. food processing, horticulture,catering, domestic or hospital environments. The invention compositionscan be used to treat crops and harvested plants or plant products.

The solutions of the invention may be used for other purposes whereperacids are used, including bleaching or as a bleach additive inwashing processes.

Having described the invention in general terms, specific embodimentsthereof are described in greater detail by way of example.

EXAMPLE 1

A solution containing 14,04 g glutaric acid, 9,79 g ethanol, 17,65 gconcentrated hydrogen peroxide (85,5% wt), 1 g concentrated sulphuricacid, 57,52 g demineralised water, 0,1 g p-hydroxy benzoic acid, 0,17 gof 1-hydroxyethane-1, 1-diphosphonic acid (Briquest ADPA 60A) wasprepared with stirring, and allowed to reach equilibrium The molar ratioof ester peracid to monocarboxylic peroxycarboxylic acid found in thesystem was 1:8, measured by HPLC.

EXAMPLE 2

A solution was prepared by mixing and stirring 16,5 g glutaric acid, 8 gmethanol, 17,65 g concentrated hydrogen peroxide (85% wt), 0,1 gparahydroxy benzoic acid, 0,2 g Briquest ADPA 60A, 1 g concentratedsulphuric acid, 56,6 g water. The solution was allowed to reachequilibrium. The molar ratio of ester peracid to monocarboxylicperoxycarboxylic acid found in the system was 1:3.

EXAMPLE 3

A solution was prepared as described in example 2 with a lower level ofmethanol, 3 g methanol in stead of 8 g, a lower level of Briquest ADPA60A, 0,17 g instead of 0,2 g, a higher level of water, 61,6 g in steadof 56,6 g. The molar ratio of ester peracid to monocarboxylicperoxycarboxylic acid found in the system was 1:11.

EXAMPLE 4

A solution was prepared by mixing and stirring 16,5 g of a mixture ofadipic, glutaric and succinic acids, 8 g of methanol, 17,65 gconcentrated hydrogen peroxide (85% wt), 1 g concentrated sulphuricacid, 56,6 g demineralised water, stabilised with 0,1 gpara-hydroxybenzoic acid and 0,17 g Briquest ADPA 60A. The solution wasallowed to reach equilibrium. The presence of esters peracids wasdetected by HPLC.

What is claimed is:
 1. A process for the production of an aqueousmonoester peroxycarboxylic acid solution by reaction of a peroxygencompound with at least one polycarboxylic acid and with at least onealcohol optionally in the presence of an acid catalyst.
 2. The processaccording to claim 1, wherein the polycarboxylic acid is a dicarboxylicacid containing up to 20 carbon atoms, and wherein the dicarboxylic acidis used in an amount from 0,05 to 65% wt.
 3. The process according toclaim 1, wherein the peroxygen compound is chosen from hydrogenperoxide, inorganic peracids, organic peracids, organic peracids,persalts, and wherein the peroxygen compound is used in an amount of0,05 to 30% wt of the reaction mixture.
 4. The process according toclaim 1, wherein the alcohol is chosen from monoalcohols and dialcoholscontaining up to 20 carbon atoms, wherein the alcohol is used in anamount from 0,05 to 45% wt of the reaction mixture and wherein the molarratio of alcohol to dicarboxylic acids is from 0,1:1 to 10:1.
 5. Theprocess according to claim 1, wherein an acid catalyst is used chosenfrom inorganic or organic acids having Pka of 3 or lower, and whereinthe acid catalyst is used in an amount from 0,05 to 10% wt of thereaction mixture.
 6. The process according to claim 1, wherein thealcohol is a polyol containing up to 20 carbon atoms, wherein thealcohol is used in an amount from 0,05 to 45% wt of the reaction mixtureand wherein the molar ratio of alcohol to dicarboxylic acids is from0,1:1 to 10:1.